There is a known rotary damper including a driven rotation member integrally formed with a rotation portion such as a gear or a rack which is engaged with a driving member, a fixing and supporting member which holds the driven rotation member rotatably, an accommodation portion, for example, in the shape of a circle, which is formed between the fixing and supporting member and the driven rotation member, a sealing member which seals an end of an outer circumference of the accommodation portion, so that the driven rotation member and the fixing and supporting member can be relatively rotated, and a viscous fluid which is stored in the accommodation portion and damps the relative rotation of the driven rotation member and the fixing and supporting member (for example, see Patent Document 1).
The rotary damper includes an opening (hole), which enables the accommodation portion to communicate with the atmosphere, in the center of the fixing and supporting member. The rotary damper prevents air from being collected in the accommodation portion at a time when the driven rotation member and the fixing and supporting member are assembled for easy assembly and prevents air from being mixed in the viscous liquid for maintaining the precision of torque.
However, since there is not a preventive plan for the leakage of the viscous liquid from the opening (hole), that is, the opening (hole) is not closed, when the rotary damper is used at a high temperature, the viscous liquid may leak from the opening (hole).
Thus, a rotary damper in which an opening (hole) which enables an accommodation portion to communicate with the atmosphere is not provided is proposed with consideration of the leakage of the viscous fluid from the opening (hole) (for example, see Patent Documents 2 to 5).
In addition, a rotary damper having a concave portion in which a convex portion of a casing fits at the center of the lower side and an air discharge path, one side of which is open for the concave portion of a rotation body and the other side of which is open for an outer circumference face of the rotation body in the rotation body rotatably disposed inside the casing filled with the viscous fluid is proposed (for example, see Patent Document 6).    Patent Document 1: Japanese Registered Utility Model No. 2603574    Patent Document 2: Japanese Examined Utility Model Registration Application Publication No. 1-37236    Patent Document 3: Japanese Patent No. 3421484    Patent Document 4: Japanese Registered Utility Model No. 2519149    Patent Document 5: Japanese Unexamined Patent Application Publication No. 11-30261    Patent Document 6: Japanese Unexamined Patent Application Publication No. 10-306836
However, when an opening (hole) which enables an accommodation portion to communicate with the atmosphere is not provided, with consideration of the leakage of the viscous fluid from the opening (hole), air is collected in the accommodation portion to make the assembly inconvenient, the air is mixed in the viscous liquid to make the damping torque non-uniform, and the precision of the torque becomes not constant (non-uniformity of the damping torque occurs).
In addition, in the rotary damper disclosed in Patent Document 6, although the air which is collected in the concave portion of the rotation body at a time when the rotation body is attached can be discharged through the air discharge path, when a capping member is attached after the attachment of the rotation body, air is trapped in the casing by the capping member.
When the air is trapped in the casing as described above, the damping torque becomes non-uniform, and the precision of the torque becomes not constant.